Bioactives from Marine Resources - ACS Publications - American

Chapter 3

Bioactives from Marine Resources

Downloaded by NORTH CAROLINA STATE UNIV on October 8, 2012 | http://pubs.acs.org Publication Date: September 1, 2008 | doi: 10.1021/bk-2008-0987.ch003

Fereidoon Shahidi Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada

Marine and cultured fish, shellfish and other species provide a rich source of food as well as by-products that could be used for production of a wide range of bioactive compounds. These bioactives include omega-3 fatty acids, proteins and biopeptides, carotenoids and carotenoproteins, enzymes, chitinous materials and glucosamine as well as calcium, among others. The bioactives present in seafoods and marine resources are effective in rendering beneficial health effects and reducing the risk of a number of chronic diseases. Thus, marine bioactives may serve as important value-added nutraceuticals, natural health products and functional food ingredients that can be used for health promotion and disease risk reduction.

Introduction Seafoods have traditionally been used because of their variety of flavor, color, texture and accessibility in the coastal areas. More recently, seafoods are appreciated because of the emergence of new evidence about their role in health promotion and disease risk reduction, primarily arising from their bioactive omega-3 fatty acids, among others. Bioactive components and nutraceuticals from marine resources belong to several classes of compounds and are used in foods and as nutraceuticals or natural health products (see Table I). When processing seafoods or during catch, a large proportion of by-products or Iow24

© 2008 American Chemical Society

In Dietary Supplements; Ho, C., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

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value fish is produced. The components of interest that could be extracted or produced from marine resources include lipids, proteins and biopeptides, minerals, flavorants, carotenoids and carotenoproteins, enzymes, chitinous materials and other specialty products. The importance of omega-3 fatty acids, bioactive peptides, glucosamine, chitosan and chitosan oligomers and other bioactives in food and non-food applications as well as for health promotion purposes has been well recognized. This chapter provides a cursory account of selected bioactives from marine resources.

Table I. Nutraceuticals and Natural Health Products for Marine Resources Application Area Components Chitin, chitosin, chitosan, oligomer, Food, water and juice clarification, glucosamine agriculture, supplements Omega-3 oils

Nutraceuticals, immune enhancement, etc.

Chonodostin sulfate

Dietary supplement, arthritic pain

Squalene

Skin care

Biopeptides, collagen and protein

Nutraceuticals, immune enhancement, etc.

Carotenoids and Carotenoprotein

Nutraceuticals, etc.

Minerals (calcium)

Nutraceuticals

Enzymes

Food and speciality application, etc.

Other specialty chemicals

Miscellaneous

Specialty and Nutraceutical Lipids The occurrence and health benefits of long-chain omega-3 polyunsaturated fatty acids (PUFA) in seafoods and other marine organisms is a well established fact (1-3). These fatty acids are produced in phytoplanktons in the oceans and are then consumed by fish and other marine species. Thus, omega-3 P U F A may be procured from marine algae, body of fatty fish, liver of white lean fish and the blubber of marine mammals. The constituent fatty acids present in such oils include eicosapentaenoic acid (EPA, C20:5n-3), docosahexaenoic acid (DHA, C22: 6n-3), and to a lesser extent docosapentaenoic acid (DPA, C22: 5n-3) in different proportions, depending on the species involved. In addition, liver oil from white lean fish serves as an excellent source of vitamin A while that of shark has a high content of squalene and other bioactives. Table II summarizes the fatty acid composition of selected marine oils and an algal oil produced commercially. As can be seen, the contents of E P A , D H A



26 and D P A in each oil is dependent on the source material. Thus the ratio of E P A to D H A in menhaden, cod liver and seal blubber oils varies considerably, but the algal oil tested almost exclusively contained D H A . Furthermore, positional distribution of omega-3 fatty acids in such oils, again, depends on source material. The omega-3 fatty acids are primarily located in the sn-2 position of triacylglycerols while they are present mainly in the sn-1 and sn-3 positions of seal blubber oil. Marine oils, similar to other edible oils, are subjected to different processing steps of refining, bleaching and deodorization. As protective components of oils are generally removed to a large extent during processing, it is important to treat the resultant refined, bleached and deodorized (RBD) oils with appropriate antioxidants in order to enhance their oxidative stability. Microencapsulation provides another means for extending the shelf-life of highly unsaturated oils. Regardless, such oils increase the body demand for vitamin E . Therefore, addition of vitamin E , usually in the form of mixed tocopherols, to highly unsaturated oils is necessary for enhancing their oxidative stability and also to augment the body's need for vitamin E. The use of marine oils containing omega-3 fatty acids is recommended for foods that are used within a short period of time in order to avoid possible offflavor development during their expected shelf-life. While it is possible to mask some of the off-flavors generated due to production of flavor-active secondary oxidation products, presence of primary products of oxidation remains to be a concern. Another way of introducing omega-3 fatty acids into food products is to employ adequately microencapsulated products that may remain intact until they reach the gastrointestinal tract. In this way, there is no flavor effect on the product even i f the oil used initially contained some oxidation products. Table III summarizes a number of food products that are usually selected to enrich them with omega-3 oils. The beneficial health effects of marine oils are manifold, but include coronary heart disease (CHD), visual and cognitive development, psychiatric conditions, inflammatory diseases, Crohn's disease and type 2 diabetes, among others. The omega-3 fatty acids, especially D H A , are known to dominate the fatty acid profile of brain and retina lipids and play a major role in the development of the fetus and infants as well as health status and body requirement of pregnant and lactating women. For therapeutic purposes, the natural sources of omega-3 fatty acids as such may not provide the necessary amount of these fatty acids and hence production and use of omega-3 concentrates may be required (4). The omega-3 concentrates may be produced in the free fatty acid, simple alkyl ester, and acylglycerol forms. To achieve this, physical, chemical and enzymatic processes may be employed for concentrate production. The available methods suitable for this purpose, on an industrial scale, are low-temperature crystallization, fractional or molecular distillation, urea complexation, chromatography,


27 Table II. Major Fatty Acids of Omega-3 Rich Marine and Algal oils*


Fatty acid 14:0 16:0 16:1 n-7 18:0 18:1 n - 9 , n - l l 20: n-9 20:5 n-3 22:1 n-11 22:5 n-3 22:6 n-3

Menhaden

Cod liver

Seal blubber

Algal

8.32 17.4 11.4 3.33 12.1 1.44 13.2 0.12 2.40 10.1

3.33 11.0 7.85 3.89 21.2 10.4 11.2 9.07 1.14 14.8

3.73 5.58 18.0 0.88 26.0 12.2 6.41 2.01 4.66 7.58

14.9 9.05 2.20 0.20 18.9

0.51 47.4

* Units are weight percentage of total fatty acids; algal oil is DHASCO (docosahexaenoic acid single cell oil).

supercritical fluid extraction, and enzymatic splitting, among others (5). These procedures have been used, albeit to different extent, by the industry to prepare concentrates that are often sold in the ethyl ester form or re-esterified with glycerol to be offered as triacylglycerols to the market. However, it has been demonstrated that acylglycerols are more stable than their corresponding ethyl esters. Regardless, the modified oils need to be stabilized using synthetic or preferably natural antioxidants. In preparation of modified lipids containing omega-3 fatty acids, structured lipids (SL) may be produced. S L are triacylglycerols (TAG) or phospholipids (PL) containing combinations of short-chain, medium-chain and long-chain fatty acids (SCFA, M C F A and L C F A , respectively) located in the same molecule and may be produced by chemical or enzymatic means (6,7). Structured lipids are developed to fully optimize the benefits of their fatty acid constituents in order to affect metabolic parameters such as immune function, nitrogen balance, and lipid clearance from the bloodstream. These specialty lipids may be produced via direct esterification, acidolysis and hydrolysis or interesterification. We have used acidolysis process to incorporate capric acid or lauric acid into seal blubber oil (8,9). In addition, we produced 91% gamma-linolenic acid ( G L A ) concentrate from borage oil (10) which was subsequently used in acidolysis of menhaden and seal blubber oils (77). Such structured lipids that include G L A , E P A and D H A were also prepared using borage and evening primrose as a source of G L A and acidolysis with E P A and/or D H A (12,13). The products so obtained, while similar to those produced by incorporation of G L A into marine oils, differ in the composition and distribution of fatty acids involved.


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Bioactive Peptides and Proteins From Marine Resources Hydrolysis of the amide linkage in the protein chain leads to the formation of peptides with different numbers of amino acids as well as free amino acids. While enzymes with endopeptidase activity provide peptides with different chain lengths, exopeptidases liberate amino acids from the terminal positions of the protein molecules. Depending on reaction variables as well as the type of enzyme, the degree of hydrolysis of proteins may differ considerably. The peptides produced from die action of a specific enzyme may be subjected to further hydrolysis by other enzymes. Thus, use of an enzyme mixture or several enzymes in a sequential manner may be advantageous. The peptides so obtained may be subjected to chromatographic separation and then evaluated for their amino acid sequence as well as their antioxidant and other activities. In a study on capelin protein hydrolysates, four peptide fractions were separated using Sephadex G-10. While one fraction exerted a strong antioxidant activity in a P-carotene/ starch linoleate model system, two fractions possessed a weak antioxidant activity and the fourth one had a prooxidant effect. Two dimensional H P L C separation showed spots with both pro- and antioxidant effects (14). Meanwhile, protein hydrolysates prepared from seal meat were found to serve as phosphate alternatives in processed meat applications and reduced the cooking loss considerably (15). Furthermore, Alaska pollock skin hydrolysate was prepared using a multienzyme system in a sequential manner. The enzymes used were in the order of Alcalase, Pronase E , and collagenase. The fraction from the second step, which was hydrolyzed by Pronase E , was composed of peptides ranging from 1.5 to 4.5 kDa and showed a high antioxidant activity. Two peptides were isolated (Table V), using a combination of chromatographic procedures, and these were composed o f 13 and 16 amino acid residues (16). The sequence of the peptides involved is given in Table IV and compared with those of soy 7S protein hydrolysates (17). These peptides exert their antioxidant activity via free radical scavenging as well as chelation effects. Recently, proteases from shrimp processing discards were characterized (18) and application of salt-fermented shrimp byproduct sauce as a meat tenderizer was reported (19).

Chitin, Chitosan, Chitosan Oligomers and Glucosamine Chitin is recovered from processing discards of shrimp, crab, lobster, and crayfish following deproteinization and demineralization (20). The chitin so obtained may then be deacetylated to afford chitosan (20). Depending on the duration of the deacylation process, the chitosan produced may assume different viscosities and molecular weights. The chitosans produced are soluble in weak


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Table III. Food Application of Omega-3 Oils Bread/bread products

Margarine and spreads

Cereals, crackers, noodles

Eggs

Pasta and cakes

Bars and candies

Milk and dairy products, ice cream

Infant formula

Juices

Fabricated seafoods, burgers, etc.

Mayonnaise and salad dressings

Others

acid solutions, thus chitosan ascorbate, chitosan acetate, chitosan lactate, and chitosan malate, among others, may be obtained and these are all soluble in water. Chitosan has a variety of health benefits and may be employed in a number of nutraceutical and health-related applications. Chitosan derivatives may also be produced in order to obtain more effective products for certain applications. Chitosans with different viscosities were prepared and used in an experiment designed to protect both raw and cooked fish against oxidation as well as microbial spoilage (27-25). The content of propanal, an indicator of oxidation of omega-3 fatty acids, was decreased when chitosan was used as an edible invisible film in herring. Furthermore, the effects were more pronounced as the molecular weight of the chitosan increased. In addition, inhibitory effects of chitosan coatings in the total microbial counts for cod and herring showed an approximately 1.5 and 2.0 log cycles difference between coated and uncoated samples, respectively, after 10 days of refrigerated storage (results not shown). However, to have the products solubilized in water without the use of acids, enzymatic processes may be carried out to produce chitosan oligomers. Due to their solubility in water, chitosan oligomers serve best in rendering their benefits under normal physiological conditions and in foods with neutral pH. Furthermore, depending on the type of enzyme employed, chitosan oligomers with specific chain lengths may be produced for certain applications (24). The low-molecular chitin and chitosan oligomers (also known as chitin/chitosan oligosaccharides (COSs) have received considerable attention as physiologically functional materials having antitumor, immuno-enhancing and antibacterial activities (25-27). Production of COSs via the hydrolysis of chitosan may be achieved chemically or enzymatically. The enzymatic production is preferred, but cost of enzyme may be prohibitive. Therefore, a continuous low cost production method to produce COSs with desired molecular size has been developed (28). The COSs (Table V ) with low-molecular weight and hetero-chitosan oligosaccharides, have been reported to have antibacterial,


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Table IV. Antioxidative Peptides from Alaska Pollock Skin Hydrolysate and Soy 7S Protein


8

Peptide Alaska Pollock Pi P Soy 75 Protein

Amino acid sequence Gly-Glu-Hyp (Gly-Pro-Hyp) -Gly (Gly-Pro-Hyp) -Gly 3

4

2

Val-Asn-Pro-His-Asp-His-Glu-Asn Leu-Val-Asn-Pro-His-Asn-His-Glu-Asn Leu-Leu-Pro-His-His Leu-Leu-Pro-His-His-Ala-Asp-Ala-Asp-Tyr Val-Ile-Pro-Ala-Gly-Tyr-Pro Leu-Gly-Ser-Gly-Asp-Ala-Leu-Arg-Val-ProSer-Gly-Thr-Tyr-Tyr

Pi P P P P P 2

3

4

5

6

a

Adapted from Ref 16,17

Table V. Antibacterial Activity of Different Molecular Weight COS Fractions Bacteria

Antibacterial activity ( %)" LMWCOSs MMWCOSs' HMWCOSs" 51 ± 7 6 2 ± 6 98 ± 0 60 ± 2 56 ± 4 71 ± 3 89±0 88 ± 0 91 ± 2 22 ± 8 35 ± 5 47±5 99 ± 0 99±0 100 ± 0 93 ± 9 95 ± 0 97 ± 3 23 ± 1 57 ± 3 82 ± 0 63 ± 7 60 ± 5 63 ± 5 63 ± 7 67 ± 3 70 ± 0

d

e

Escheria coli EscheriacoliO-157 Salmonella typhi' Pseudomonas aeruginosa Streptococcus mutans Staphylococcus aureus Straphylococcus epidermidis Bacillus subtilis Micrococcus luteus e

6

f

f

f

f

f

a

Following the incubation of bacterial culture with 0.1% different COSs fractions, the number of colonies formed on the medium was calculated as a percentage compared to the control. High molecular weight chitosan oligosaccharides (molecular weight range 10-5 kDa). Medium molecular weight chitosan oligosaccharides (molecular weight range 5-1 kDa). Low molecular weight chitosan oligosaccharides (molecular weight below than 1 kDa). Gram-negative. Gram-positive. b

c

6

e

f



31 radical scavenging, A C E inhibitory and anticoagulant activities (29). The monomer of chitin, N-acetylglucosamine (NAG), has been shown to possess anti-inflammatory properties. Meanwhile, glucosamine, the monomer of chitosan, prepared via HC1 hydrolysis, is marketed as glucosamine sulfate. This formulation is prepared by addition of ferrous sulfate to the preparation. Glucosamine products may also be sold in formulation containing chondroitin 4and chondroitin 6-sulfates. While glucosamine helps to form proteoglycans that sit within the space in the cartilage, chondroitin sulfate acts like a liquid magnet. Thus glucosamine and chondroitin work in a complementary manner to improve the health of the joint cartilage. The byproducts in chitin extraction process from shellfish include carotenoids/carotenoproteins, and enzymes (30-33). These components may also be isolated for farther utilization in a variety of applications.

Enzymes The aquatic environment contains a wide variety of genetic material and hence represents exciting potential for discovering different enzymes (34). Therefore, much effort has been made to recover and characterize enzymes from fish and aquatic invertebrates (30). Digestive proteolytic enzymes from stomachless marine fish such as cornier, crayfish and puffer appear to inactivate polyphenol oxidize and/or pectin esterase in fruit juices. Successful application of such enzymes has also allowed inactivation of polyphenol oxidase in shrimp processing as an alternate to sulfiting (57). Alkaline phosphates from shrimp may be used in different kits and some enzymes may be recovered and used in deskinning of fish and squid or cleaning of fish roe for caviar production, among others.

Carotenoids Carotenoids and carotenoprotiens are present in salmonoid fish as well as in shellfish. These carotenoids may be recovered from processing by-products and used in a variety of applications (55). In addition, certain carotenoids, such as Fucoxanthin occur naturally in seaweeds (55,56). Fucoxanthin has been shown to have anti-proliferative activity on tumor cells and has also been implicated in having anti obesity and anti-inflammatory effects. Fucoxanthinol is a known metabolite of fucoxanthinol.


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Minerals and Calcium Among fish processing by-products, fish bone or skeleton serves as a potential source of minerals and calcium which is an essential element for human health. Calcium from fish would be easily absorbed by the body (37). However, to incorporate fish bone into calcium-fortified foods, it is necessary to first convert it into an edible form by softening its structure. This could be achieved by hot water treatment and heat treatment in an acetic acid solution. Pepsinassisted degradation of Alaska Pollock bone in acetic acid solution led to highest degree of hydrolysis and dissolution of both mineral and organic parts of fish bone (38,39). As reported by Larsen (37), the intake of small fish with bones could increase calcium bioavailability. Fish bone contains hydroxyapatite which unlike other calcium phosphates does not break under physiological conditions and takes part in bone bonding. This property has been exploited for rapid bone repair after major trauma or surgery.

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Bioactives from Marine Resources - ACS Publications - American

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